This application relates to wireless communications.
Wireless communication systems use electromagnetic radio waves to provide wireless communication services to wireless communication devices which may also be referred to as wireless nodes or access terminals, such as mobile phones and portable computers equipped with wireless communication ports. Different types of wireless communication systems have been developed to provide different wireless communication applications. A wireless local area network (WLAN) may be designed to use one or more communication devices called access points (APs) as a portal to one or more packet data and other networks and to provide wireless services for mobile and other wireless communication devices (i.e., wireless nodes) in a small geographic area. Each access point has a radio transceiver that covers a limited area called a hot spot or zone within which a wireless device can access wireless services. When multiple wireless devices or nodes access a single access point, the quality of service for different devices or nodes becomes an issue. IEEE 802.11 standards have been widely adopted as one of the communication protocols for WLANs and IEEE 802.11e has features that specifically address the quality of service in WLANs.
WLANs can be used to provide wireless broadband services such as multimedia applications which may include streaming video, teleconferencing, voice over IP and other services. The affordability and improvements to support higher data rates in WLANs have led to a wide spread adoption of WLAN technologies. This can be seen in the proliferation of WLAN networks in homes, offices, and commercial settings, such as airports and restaurants. However, the time-varying nature of wireless access and the diverse requirements of multimedia applications make the task of supporting wireless multimedia services in WLANs challenging. With the increasing demand for broadband services, there is a need to support diverse multimedia services over the wireless medium in a WLAN. Standardization efforts are being pursued to provide Quality of Service (QoS) mechanisms for medium access in WLANs.
IEEE 802.11e is an example of such efforts. As a step towards meeting multimedia application requirements in WLAN networks, the 802.11 Working Group has included in IEEE 802.11e differentiation mechanisms at the Medium Access Control (MAC) layer. See, e.g., IEEE-802.11WG, “Draft supplement to standard for telecommunications and information exchange between systems—LAN/MAN specific requirements—part 11: MAC enhancements for quality of service (QoS),” IEEE 802.11e Standard Draft/D8.0 (February 2004). The IEEE 802.11e standard provides a framework called Hybrid Coordination Function (HCF) that multiplexes between two modes of medium access provided in 802.11e: a distributed access mode under the name of Enhanced Distributed Channel Access (EDCA) and a centralized access mode under the name of Hybrid Coordination Function Controlled Channel Access (HCCA). With the distributed channel access scheme, each flow gains access to the channel through a contention-based algorithm. This method is targeted for bursty traffic flows with unknown traffic requirements. With centralized access, a polling-based scheme is used to grant access to traffic flows based on reservation requests provided by each flow. This scheme is well suited for flows that require guaranteed channel access such as real-time multimedia applications. However, in this scheme, the centralized controller requires accurate information about the flows prior to scheduling, making it more suitable for predictable traffic. The standard also presents a reference design of a scheduler to construct a polling schedule based on the flow requirements specified in the reservation request at initialization. The details of this reference design can be found in J. Prado, “Mandatory TSPEC parameters and reference design of a simple scheduler,” IEEE 802.11-02/705ar0, November 2002.